A colleague of mine recently posted a link to this 2015 article on Create your own MD5 collisions and while this is hardly news, and so I haven't bothered to see if the instructions still work, I thought I'd share it both because the sample result looks like it could be fun and because of this remark:
I promise it does not mine bitcoins in the background although thinking about it this would be a good scam and I may introduce this functionality.